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*RACS ENT Fellowship > VIVA – Anatomy – Otology > Flashcards

VIVA – Anatomy – Otology Flashcards

1
Q

Define Hypotympanum

A

Below a horizontal line level with inf margin of annulus

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2
Q

Define Protympanum

A

Vestibule to ET à leads to ET

Ant to a vertical line level with ant margin of annulus

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3
Q

Define Epitympanum

A

Above a horizontal line level with sup margin of annulus

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4
Q

Define Posterior tympanum

A
  • post to a vertical line level with post margin of annulus
  • includes sinus tympani + facial recess
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5
Q

What are the boundaries for
Supratubal recess

A

= ant epitympanum / Anterior tympanic recess

Ant Ant petrosal tegmen

Post Cog (from cochleariform process to tegmen)

Sup MCF

Lat Tympanic bone, chorda tympani

  • bordered medially by the geniculate fossa and the anterior portion of the tympanic facial nerve canal, and laterally by the petrosquamosal suture
  • partitioned in varying degrees in some temporal bones from the protympanum by a horizontal mucosal fold at the level of the tensor tympani muscle, or in others from the epitympanic space proper by a vertical fold attached to the cog
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6
Q

What are the boundaries of Sinus tympani

A

Sup Ponticulus (from pyramidal eminence) + LSCC

Post PSCC

Inf Subiculum, styloid eminence, jugular wall

Med Bony labyrinth

Lat Pyramidal eminence + facial nerve

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7
Q

What are the boundaries of Facial recess

A

aka suprapyramidal recess

Med Facial nerve + styloid complex

Lat tympanic bone

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8
Q

What are the boundaries of MacEwen’s triangle

A

Antrum lies 15mm below 2mm at birth

Then grows 1mm per year till adult depth at puberty

Boundaries temporal line (aka supramastoid crest, linea temporalis)

Post wall of EAC

Sup wall of EAC

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9
Q

Point to on a bone and name the contents of Tympanomastoid fissure

A

Tympanomastoid suture Contains Arnold’s nerve

Route of spread from EAC to skull base

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10
Q

Point to on a bone and name the contents of Tympanosquamous fissure

A

Anterosuperior to EAC

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11
Q

Point to on a bone and name the contents of Petrotympanic fissure


A

Divided into 2 branches by intertympanosquamosal crest

Ant Anterior PS fissure → cranial cavity à veins to inferior petrosal sinus

Post Anterior TP fissure

(True glasserian fissure)→ glenoid fossa

Contents ant tympanic a + v

Ant malleolar lig (continuation of sphenomandibular lig)

Chorda tympani (in canal of Huguier)

Route of spread from ME to Infratemporal fossa

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12
Q

What are the attachments to the mastoid tip? Where do they attach?

A

Lateral SCM, Post auricular, occipital

Medial Post belly of digastric

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13
Q

What is the name and contents for the foramen on the mastoid tip?


A

Mastoid foramen Contains Emissary vein

Mastoid br of occipital artery

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14
Q

Point to the IAC

What angle does it make with the sagittal plane?

A

80-90 deg to sagittal (in 60%), 90-100 deg (in 40%)

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15
Q

What angle does IAC make with the longitudinal axis of the TB?

A

45 degrees

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16
Q

Diameter IAC?

A

<2mm suggests aplasia of nerves

Usually 4mm

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17
Q

Length IAC?


A

Length of 6-9mm

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18
Q

Contents IAC?


A
  • nervus intermedius
  • facial motor root
  • cochlear nerve
  • inferior vestibular nerve
  • superior vestibular nerve
  • labyrinthine artrey
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19
Q

Draw and label the structures at the fundus oof IAC

A
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20
Q

What are the relations of the nerves of the IAC At the brainstem?

A

The facial nerve is a round structure located anterior to the vestibulocochlear nerve. Moving laterally in the IAC, it courses anterosuperior to the vestibulocochlear nerve until it leaves the canal. The cross section of the vestibulocochlear nerve as it leaves the brain stem is most frequently rectangular or crescentic. It divides completely into the superior, inferior, and vestibular nerves and the cochlear nerve only in the most lateral portion of the IAC

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21
Q

What are the relations of the nerves of the IAC At the porus?

A
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22
Q

Point to the subarcuate fossa

Contents?

A

above and lateral to IAC

Leading to petromastoid canal

  • runs in the middle of the SSCC
  • post fossa sup lat to IAC → non ampullated end of SSCC
  • (5% opens into mastoid antrum)
  • Contents Subarcuate vessels
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23
Q

What is the lip of bone that overhangs at the subarcuate fossa?

A

Operculum

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24
Q

Point to the vestibular aqueduct


What are the contents of the facial hiatus?

A

Ant to SCC

= dehiscence marking the entrance of GSPN into the MCF

Contents GG

GSPN

Superficial petrosal branch of middle meningeal artery

Sometimes Facial nerve itself may lie within

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25
Q

Identify the superior tympanic canaliculus

A
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26
Q

Contents of superior tympanic canaliculus?


A

Located in the petrosquamous fissue

From the middle ear inf to cochleariform process to MCF

Contents LSPN

Superior tympanic artery (from middle meningeal)

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27
Q

Identify the inferior tympanic canaliculus

A
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28
Q

Contents inferior tympanic canaliculus?


A

In the ridge (petrosal fossa) dividing carotid canal and jugular fossa

Contents Jacobson’s nerve

Inf tympanic vessels (br of ascending pharyngeal artery)

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29
Q

Identify the mastoid canaliculus

Contents?


A

Lateral wall of jugular foramen

Contents Arnold’s nerve (aka Alderman’s nerve)

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30
Q

Identify the stylomastoid foramen

Contents?


A

Contents CN VII

Stylomastoid artery (br post auricular)

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31
Q

Identify the musculotubular canal

Define the following

Caroticotympanic canaliculi

A

From carotid canal to ME

Contents caroticotympanic arteries

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32
Q

Define the following - Hyrtl’s fissure


A

Tympanomeningeal fissure

Connects hypotympanum (inf to RW) to post fossa

Parallels cochlea aqueduct

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33
Q

Define the following - Fissula ante fenestram

A

bt the vestibule ant to OW + periosteum of ME next to cochleariform process

May be appendage of perilymphatic space

Formed by resorption of precartilage

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34
Q

Define the following - Fissula post fenestram

A

Invagination into otic capsule post to OW

Extends 1/3 towards non ampullated end of LSCC

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35
Q

Define the following - Cochlea aqueduct? Significance?

A

transmits perilymphatic duct (aka periotic duct)

From scala tympani in basal turn to cochlear canaliculus in pyramidal fossa (ant compartment of jugular foramen)

Significance Root of spread of meningitis (explains labyrinthitis ossificans)

Perilymph oozer if abnormally patent

Surgical landmark for CNIX when performing translab

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36
Q

Define the following - Paravestibular canaliculi

A

Accessory canals

Canal of Cotugno for inf cochlear vein (+/- artery)

2nd canal vein from ME to canal of Cotugno

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37
Q

Define the following - Koerner’s septum

Significance?

When should you suspect it?

A

= remnant of petrosquamous suture line from downgrowth of squamous cells to form the mastoid tip (note: also post extension of the Cog)

Divides mastoid into superficial squamous

Deep petrosal

Parts open separately into the antrum

Should be considered if antrum is

Difficulty to find

Small and constricted

Appears to be in an anomalous position

Clinical significance

  • Failure to recognise it’s presence may lead to dissecting inferiorly at this level and CN VII injury
  • Barrier to spread of infection bt medial and lateral mastoid
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38
Q

Define the following - Trautmann’s triangle

A

= area of post fossa dura

Potential weak spot for spread of mastoiditis to post fossa

Boundaries Sigmoid sinus

Sup petrosal sinus

Bony labyrinth

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39
Q

Define the following - Donaldson’s line

A

= line from LSCC to bisect the PSCC

Endolymphatic sac lies inferior

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40
Q

Define the following - Arnold’s nerve - What cranial nerve(s) contribute to it? What is it’s pathway?
What does it supply?

A

= CNX + CNIX + CN VII

From jugular (superior vagal) ganglion

Joined by filament of petrous (inferior Glossopharyngeal) ganglion (CN IX)

Small cutaneous branch of CN VII

Passes behind IJV

Enters mastoid canaliculus (lateral wall of jugular fossa)

Runs through TB, crosses facial canal 4mm above stylomastoid foramen

Travels through tympanomastoid suture (bt mastoid process + tympanic bone)

2 branches br to post auricular n

Br to post auricle + post EAC

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41
Q

LSPN What nerves contribute to it? What is it’s pathway?
What does it supply?

A

= Jacobson’s nerve + (usually 2) caroticotympanic sympathetic nerves

Enters superior tympanic canaliculus (beneath cochleariform process)

Note: joined by a small twig from the facial (as it passes GSPN) + also sends branches to GSPN

To otic ganglion à parasympathetic supply to parotid

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42
Q

What are the 3 vestibular anastomoses?


A

Voit’s SVN to sup part of macula of saccule

Vestibulofacial SVN to CNVII

Oort’s Saccular nerve to cochlear nerve

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43
Q

Name the pathways of spread of infection from

CSF to Inner ear

A

through IAC fundus

Modialar end defects

Cochlear aqueduct

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44
Q

Name the pathways of spread of infection from

CSF to middle ear

A

Hyrtl’s fissure (congenital cleft bt hypotympanum + PCF)

Petrosquamous sinus (of Lushka)

Occasional embryological remnant

esp. open in infancy, usually obliterated by 6/12

Very variable (Usually connects ME + TV or sigmoid sinus)

Usually empties into deep temporal vein

Retrograde spread Internal auditory vein

Mastoid emissary vein

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45
Q

Name the pathways of spread of infection from

Inner to middle ear

A

Oval window

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46
Q

Describe the mucociliary tracts of the ME


A

Hypotympanic→ ET

Epitympanic → ET

Promontory → ET

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47
Q

What things do you look for on CT for COM?


A

Is there a cholesteatoma? If so where?

Any complications? PLF

LSCC fistula

Dehiscence tegmen

Facial nerve

Mastoid healthy or diseased? Size?

What is the state of the ossicular chain?

Is the EAC eroded?

How well aerated is the ME?

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48
Q

What things do you look for on CT in cholesteatoma?

A

Nondependent, homogenous mass associated with bone erosion or ossicular destruction is cholesteatoma in 90%, but only 50% present like this

Look for Erosion of scutum (aka shield of Leahy)

Tegmen dehiscence (present in 6% of normal)

LSCC dehiscence

Facial nerve dehiscence

Tissue in the sinus tympani

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49
Q

How many orifices from the SCCs open into the utricle?

A

5

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50
Q

Draw the cross section of the cochlea 


A
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51
Q

Discuss the function of the Stria vascularis

A
  • on the inner surface of the spiral ligament
  • stratified epithelium (3 cell Types) with intraepithelial capillaries
    • Marginal Cells à endothelial cell à Active layer facing endolymph. Maintain endocochlear potential à nuclei close to endolymphatic surface with large basal extensions which interdigitate with the intermediate cells à makes direct contact with blood vessels outside the basement membrane
    • Intermediate ells – don’t extend to endolymph surface – abut blood vessels and send tentacle like extensions between folded marginal cell processes – from migrating melanocytes of neural crest
    • Basal Cells (adjacent to spiral ligament – tight junctions separate)
  • Responsible for maintaining the electrochemical gradient (high K+)
  • Extend from spiral prominence to Reissner’s membrane

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52
Q

Discuss the function of the Spiral ligament


A
  • Thickened modified periosteum
  • Lines the lateral wall of the cochlea duct
  • Extends into both the scala vestibule and tympani à forms lat communication channel between 2 perilymph channels
  • Contains fibroblasts and connective tissue (type I collagen) (+? Cells rich in ion-transporting enzymes)
  • Provides for external attachments of basilar membrane, stria vascularis and Reisser’s membrane
  • Lined by stria vascularis, spiral prominence and external sulcus cells
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53
Q

Discuss the function of the Hensen cells


A
  • Tall columnar cells – increasing in height toward cochlear apex
  • Next to 3rd row of Deiter’s cells
  • ?Claudius cells that migrated
  • ?part of K+ recycling pathway
  • express water channel protein aquaporin 4
  • Undifferentiated cells that support the outer end of the tectorial membrane.
  • Numerous microvilli, lack of organelles
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54
Q

Discuss the function of the Dieters cells


A
  • Supporting cells of outer hair cells.
  • Lie on Basilar membrane (large cell bodies)
  • Have a cup-like opening in which the OHC’s sit
  • Contain bundles supporting filaments which originate above basilar membrane à some extend to supporting cup and others through Nuel’s space to apices of OHC to help form reticular membrane
  • Give off pharyngeal process which joins the 4 OHC’s into the reticular lamina à fills space between apical portions of OHC
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55
Q

Discuss the function of the Boetchers cells

A
  • Occur in clusters between the Claudius cells and the basilar membrane
  • Dark stain – multiple organelles
  • More common at base – not in apical turnCuboidal and arranged in single layer
  • ? produce amorphous substance of the basilar membrane
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56
Q

Discuss the function of the Claudius cells


A
  • fill the outer sulcus.
  • Continuous layer from the spiral prominence to the organ of corti
  • Large pale cells
  • Joined by tight junctions and separate the endolymph and perilymph
  • Strong expression of Na+ channels
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57
Q

Discuss the function of the Border cells of Held

A
  • Bordering inner spiral tunnel
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58
Q

Discuss the function of the Huschke’s teeth cells

A
  • Lines spiral limbus
  • Tectorial membrane attached to
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59
Q

Discuss the function of the Limbus interdental cells

A
  • Produces tectorial membrane
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60
Q

Discuss the function of the Habenula perforate

A
  • perforations along the tympanic lip of the spiral lamina giving passage to the cochlear nerves
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61
Q

Discuss the function of the Reticular lamina

A
  • From processes of Deiter cells and pillar cells
  • Fills the gaps btw the cuticular plates of the hair cells.
  • Provides tight closure between endolymphatic surface of Organ and interior extracellular spaces
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62
Q

Point to the ET on the base of skull 


A
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63
Q

What is the other canal for next to eustachian tube?

A

Thin superior bony septum separates from tensor tympani

Medial wall adjacent carotid canal (thin bone separating these structures has dehiscence’s that allow the passage of caroticotympanic arteries)

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64
Q

Length eustachian tube?

A

31-38mm long

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65
Q

Proportions eustachian tube?

A

Lateral 1/3 bony, medial 2/3 cartilaginous

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66
Q

Angles eustachian tube?

A

Slopes forward and medially 45°, down at 30°

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67
Q

eustachian tube Muscles, where do they attach?

A
  • Tensor Veli Palatini
    • Primary dilator of ET
    • Origin: Scaphoid fossa, lateral cartilaginous lamina; spine of the sphenoid bone; salpingopharyngeal fascia
    • Course: Runs inferiorly becoming a tendon that sweeps medially around the pterygoid hamulus
    • Insertion: Soft palate
    • Action: Tubal opening by drawing the lateral cartilaginous lamella inferiorly
    • Continuous with tensor tympani
    • Innervation: Mandibular nerve
    • Medial bundle of fibres most important due to attachment to the lateral wall of the cartilaginous ET
      • Pulls down on the tube and opens
  • Levator Veli Palatini
    • Loose fibrous attachments to cartilaginous TE
    • Likely aids opening
    • Origin: Inferior aspect of petrous bone, medial cartilaginous lamina
    • Course: Runs inferiorly parallel to the tube
    • Insertion: Soft palate
    • Action: Elevates the eustachian tube widening the lumen
    • Innervation: Pharyngeal plexus (CN X)
  • Salpingopharyngeus
    • Origin: Inferior aspect of the medial cartilaginous lamina
    • Insertion: Posterior pharyngeal wall, thyroid cartilage (superior horn)
    • Innervation: CN X
  • Tensor Tympani
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68
Q

Histology eustachian tube?

A
  • Simple low columnar at tympanic end to pseudostratified at nasopharynx end
  • Cilia beat towards nasopharynx
  • Mucosa of cartilaginous end has glands (absent in bony portion) and lymphoid aggregates
    • Mucous glands
    • Lymphoid tissue
  • Loose folds of mucous membrane gently occlude the cartilaginous tube in most people
    • Part during swallowing
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69
Q

How is eustachian tube different in cleft palate?


A
  • In cleft palate muscles are often hypoplastic, misdirected and have abnormal insertions
  • In cleft à aponeurosis of TVP inserts onto bony edges of cleft rather than post edge of hard palate à more anterior à soft palate shorter
  • Hypoplasia of the lateral cartilage relative to medial
  • Abnormal curvature of the tubal cartilage
  • Different width and angulation of skull base
  • Abnormal insertions of TVP and levator veli palatine – no insertion of TVP into lat cartilage in 40%, length of muscle inserted decreased
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70
Q

What are the differences in eustachian tube in infants and elderly?


A
  • Uniformly smaller
  • Horizontal orientation
  • Reaches adult dimensions at orifaces by age 4 and in length by 7
  • Higher ratio of cartilaginoug to bony portion in children (8:1)
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71
Q

What is the tonsil of Gerlach?


A

Collection of lymphoid nodules near the pharyngeal opening of the auditory tube

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72
Q

What is the blood supply of the ET?


A
  • Ascending Pharyngeal artery
  • Maxillary
    • Superior tympanic branch of Middle meningeal Artery
    • Pharyngeal branches
    • Artery of Pterygoid canal (off SPA)
  • Facial
    • Ascending palatine branch
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73
Q

What are the functions of the ET?

A
  1. Regulation of ME pressure with reference to atmospheric pressure
    • Opening allows passive exchange of air between ME and Nasopharynx à equalise pressure
    • During swallowing, muscles that dilate ET activated à as soft palate elevated à TVP isometrically contracts à pulls on lateral lamina
    • Airflow is intermittent
      1. Lasts 0.2s
      2. Occurs every 1-2min
    • Gas exchange between the ME and Mastoid is also a factor
      1. Regulation is poorly understood
      2. Inflammed mucosa transports gases more readily than normal mucosa
      3. Well pneumatised mastoid may “buffer” changes in the ME
  2. Clearance of Middle ear secetions
    • Active process via mucociliary clearance
    • Ciliated cells and goblet cells increase in number on the floor and towards the nasopharynx
  3. Protection of the middle ear from sound pressures and accumulations of nasopharyngeal secretions
    • Can remain closed at pressures up to 130mmHg on the nasopharyngeal side
    • ME pressure of ~30mmHg greater than the nasopharynx open the tube
    • Secretes molecules of innate immunity eg lysozyme
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74
Q

What are the key manoeuvres and the ant limits of access for Fisch Type A?

A

= facial nerve transposition

  • radical mastoidectomy – remove air tracts lat and adjacent to otic capsule à stapes superstructure removed + ET obliterated
  • skeletonize and freed of its bony canal from the geniculate ganglion to stylomastoid F (at 2nd genu, only drill on tympanic side of nerve to avoid injury to LSCC)
  • at SMF, elevate nerve with surrounding soft tissue to prevent devascularisation
  • new bony canal drilled in anterior wall of epitympanum
  • facial nerve gently elevated and transposed into the new groove and secured within the parotid soft tissue
  • gentle handling, diamond burr, irrigation, no stretching of facial N, intraoperative monitoring
  • occlude the sigmoid sinus à ligation below mastoid emissary vein
  • expose jugular bulb and ICA
    • styloid process fractured with ICA protected
    • bone removed over ICA and below otic capsule
  • tumour removal
  • closure
    • fascia lata for dural defect
    • abdominal fat for obliteration
    • temporalis muscle rotated inferiorly to reinforce
    • routine skin closure
    • pressure dressing 5 days
  • Advantage
  • best access of all approached for jugular fossa and ICA at the skull base
  • access to jugular bulb, vertical petrous carotid and posterior infratemporal fossa
  • Disadvantages
  • longer procedure
  • maximal conductive hearing loss
  • facial nerve injury with transposition
75
Q

What are the key manoeuvres and the ant limits of access for Fisch Type B

A
  • access to petrous apex, clivus and superior infratemporal fossa
  • facial N transposition not usually needed
  • same as above
  • reflection of temporalis muscle allows the retractor to expose the superior ITF with dislocation of the TMJ inferiorly
  • risk of stretch injury of VII so still should use facial N monitor
  • limits of exposure are
    • MCF
    • mandibular condyle
    • reflected temporalis
  • need to transect middle meningeal artery and V3
76
Q

What are the key manoeuvres and the ant limits of access for Fisch Type C

A
  • an anterior extension of Type B approach
  • allows posterlateral access to rostral clivus, cavernous sinus, sphenoid sinus, peritubal space, PPF, nasopharynx in addition to those areas exposed in Type B
  • can access anteriorly up to F. lacerum up to the posterior aspect of the maxillary sinus and nasopharynx
  • can remove orbitozygomatic segment of bone and mandibular head and condyle for access
  • reconstruct with temporalis muscle flap, temporoparietal fascia flap, free flap
77
Q

What are the layers of the meninges?

A
  • Interior of cranium lined with dural mater
    • Inner and outer layers
    • Folds of the inner layer also project into the cranial cavity
      • Tentorium Cerebelli
      • Falx Cerebri
      • Diaphragma Sellae
      • Function to minimise rotatory movement of the brain
  • Surface of the brain covered with Pia Mater
  • Between the above lies the Arachnoid mater
    • Connected to Pia by filamentous processes that cross the subarachnoid space

Subarachnoid space is filled with CSF

78
Q

Pinna - Draw & Name the parts


A
79
Q

Pinna Embryology?

A

Pinna begins development in 6th week of gestation (?5)

Auricular Hillocks of His: mesenchymal tissue at the dorsal end of the 1st and 2nd branchial arches - mesoderm

6 Hillocks- 1-3= 1st branchial arch hillocks(superficial temporal a), 4-6= 2nd branchial arch hillocks (posterior auricular a) – fuse by week 12

  • 1=anterior ear lobe
  • 2= tragus
  • 3=ascending helix
  • 4+5= antihelix
  • 6= posterior lobe

Cartilage forms week 7

Concha derived from ectoderm forming EAC

Helical margin may develop separately from a skinfold caudal to hillocks 4 and 5 à develops rapidly weeks 8-12 à helix furls during 6 month

Anti-helix furls weeks 12-16 à failure to do so results in protruding scapha

Lobule is one of the last parts to development by the end of the 3rd month of gestation

Initially positioned anteriorly but is drawn posteriorly and superiorly as mandible develops (wks 8-12)à adult location week 20

80
Q

What parts form which of Pinna?

A
81
Q

Blood supply pinna?


A
  • Posterior Auricular Artery – medial
  • Superficial Temporal Artery - lateral
82
Q

Nerve supply pinna?

A
83
Q

EAC Length?

A
  • Concha to tympanic membrane
    • 25 mm long posterior wall.
    • 31 mm long anterior wall
    • 7-9mm width
84
Q

EAC Proportions?

A
  • Lateral cartilaginous (1/3) and medial osseus meatus (2/3)
    • Slight “S” bend
    • Laterally it is convex anteriorly and medially it is convex posteriorly
    • Lumen is an irregular ellipse with long axis vertical laterally and horizontal medially
      • Isthmus lies between
85
Q

EAC Constrictions?

A

There are two constrictions.

(i) The junction of bony and cartilaginous canal
(ii) Isthmus. It is the narrowest part of the external auditory canal and is about 5 mm from the tympanic membrane. Medial to Isthmus is anterior recess

86
Q

EAC Blood supply?


A
  • Posterior Auricular Artery – Auricular branch
  • Superficial Temporal Artery – Anterior Auricular
  • Deep Auricular Artery (Maxillary) – deep aspect EAC
    • Enters via Tympanosquamous suture suture
87
Q

EAC Routes of infection spread?

A

Fissures of Santorini

2-3 vertical fissures in cartilaginous anterior wall give mobility

Pathway for spread of disease to TMJ, parotid and adjacent tissues

88
Q

TM Layers?


What are the layers of the epithelial layer?

A
  • 3 layers in pars tensa
    • Cutaneous outer layer - stratified squamous
    • Middle fibrous (outer radial and inner circular collagen fibres)
      • In pars flaccida – collagen more random orientation

Inner varies from simple squamous or cuboidal to pseudostratified columnar. (Low columnar epithelium)

  • Pars flaccida is thicker than tensa à attached directly to petrous at tympanic notch à epidermis here composed of 5-10 layers of desquamating epithelial cells
89
Q

TM Blood supply?


A
  • Inner and outer systems that anastomose significantly
  • Cutaneous
    • Deep auricular branch of internal maxillary
  • Mucosal Surface
    • Anterior tympanic branch of internal maxillary
    • Stylomastoid branch of posterior auricular artery
90
Q

TM - Angle that it makes with the canal?

A
  • 55o with floor of EAM, 140o with roof
  • Faces downwards, forwards and laterally
91
Q

Boundaries of the sinus tympani?


A
  • Between bony labyrinth medially and pyramidal eminence and facial nerve laterally
  • Limited superiorly by ponticulus and lat SCC, posteriorly by post SCC and inferiorly by subiculum
92
Q

What are the eminences of the post wall of the ME?

A
  • Pyramidal eminence
    • Below fossa incudis
    • Medial to posterior canaliculus (chorda)
    • Contains stapedius muscle tendon
  • Chordal eminence
    • Contains chorda tympani
  • Styloid eminence
93
Q

What are the ridges of the post wall of the ME?

A
  • Subiculum
    • Between styloid eminence and posterior lip of round window niche
    • Separates round window from sinus tympani
  • Ponticulus
    • Between promontory (inferior margin of oval window niche) and pyramidal eminence
    • Separates posterior tympanic sinus from sinus tympani (and oval window from sinus tympani)
  • Chordal ridge
    • Between chordal and pyramidal eminences
    • Separates facial sinus from lateral tympanic sinus
  • Styloid ridge
    • Between chordal eminence and styloid eminence
  • Pyramidal ridge
    • Between styloid eminence to pyramid
94
Q

What comes out from Post ME wall eminences?


A

Chordal eminence = chorda

Pyramidal eminence = stapedius muscle tendon

95
Q

What is the name for the deficiency in the tympanic bone?


A

? Deficient superiorly at the notch of rivinus

?Foramen Huschke

96
Q

What are the dimensions of the oval window and footplate?


A

Oval window. 3.25 mm long and 1.75 mm wide (0.2 mm greater than footplate).

97
Q

Describe the layers of the membrane that covers the fenestrae cochlea

A

Round window. Faces inferior and posterior. Niche is triangular.

Membrane lies almost horizontal in roof of niche, 2.30mm x 1.87mm (average). Has 3 layers (inner mesothelial, middle fibrous and outer mucosal).

98
Q

What is the landmark for the singular nerve in the ME?


A

Singular nerve is 1mm from posteromedial attachment of the round window membrane.

99
Q

Draw the medial wall of the ME


A
100
Q

Define Prussak’s space


A

Post compartment of epitympanum

bound

  • laterally by pars flaccida (attached superiorly along edge of notch of Rivinus
  • medially by neck of malleus
  • above by lateral mallear ligament
  • below by the lateral process of the malleus

Opens posteriorly into epitympanum

101
Q

Describe the blood supply of the middle ear


A

Numerous very small arteries, mostly derived from ECA

Superior tympanic artery and inferior tympanic artery though tympanic canaliculus

  • Anterior tympanic artery
    • From maxillary via petrotympanic suture (glasserian)
    • Gives rise to 3 branches
      • Superior à bone and mucosa of ant and lat walls of epitympanum
      • Posterior à lat walls of epitympanum
      • Descending à medial aspect tm
      • Ossicular à malleus (lat mallear ligament to neck) and incus
  • Stylomastoid artery
    • From post-auricular or occipital via stylomastoid foramen
    • Terminates by anastomosing with superficial petrosal
    • Supplies facial nerve, mucosa of adjacent mastoid, otic capsule, stapedius
    • gives off posterior tympanic artery à leaves canal through canaliculus with CT à supplies posteroinferior tympanic cavity
  • Tubal artery
    • Branch of accessory meningeal via ET to supply protympanum
  • Cariotympanic arteries
  • Superior tympanic artery
    • From middle meningeal
    • Enters adjacent to LSPN through superior tympanic canaliculus
    • Supplies tensor tympani, medial half of roof, medial wall epitympanum
    • Anastomoses with inferior tympanic à gives rise to anterior stapedial artrey
  • Inferior tympanic
    • Branch of ascending pharyngeal;
    • Enters with Jacobsens nerve in inferior tympanic canaliculus
    • Ascends over promontory and anastomoses with superior tympanic and cariotympanic
    • Supplies mucosa and bone of hypotympanum and promontory
  • Deep auricular à TM
  • Superficial petrosal artery
    • From middle meningeal
    • Enters facial hiatus adjacent to GSPN
    • Anastamose with superior tympanic and branches to accompany both directions of CN VII
  • Arteries of incudostapedial area
    • Derives in part from superior and inf arteries of stapedial tendon and from posterior crural artery

All of these originate from arterial plexus within fallopian canal à supplied by superior petrosal and stylomastoid artery

102
Q

What are the routes of spread of attic cholesteatoma?


A

Post. attic cholesteatoma (commonest)

  • Via sup. incudal space à lateral to incus à antrum / mastoid
  • Via post. pouch of VT à post. tympanum (stapes, facial sinus, sinus tympani, round window)

Ant. attic cholesteatoma (least common)

  • Via ant. pouch of VT à ant. mesotympanum or supratubal recess (horizontal 7th CN & geniculate ganglion at risk)
103
Q

Draw an incus


A
104
Q

How would you shape bone for an incus interposition?


A
105
Q

What are the relations between the footplate and inner ear structures?

A

Distance from footplate to saccule; 0.75mm superiorly, 1mm in middle and 1.6mm inferiorly.

Distance from footplate to utricle; 0.5mm superiorly, 1.25mm in middle and 1.6mm inferiorly.

Shortest distance found by Anson and Donaldson is 0.82mm to saccule and 0.38mm to the utricle.

106
Q

Why is stapedotomy in Meniere’s dangerous?

A

Often causes permanent profound hearing loss – endolympathic hydrops

107
Q

What are the inputs and outputs of the tympanic plexus?


A

Tympanic plexus

  • Tympanic branch of CN IX (Jacobson’s nerve)
    • Arises from inferior ganglion of CN IX
    • Enters via inferior tympanic canaliculis b/w jugular and carotid canals
  • SNS via internal carotid nerve
    • Enters via cavity in wall of carotid canal
  • May have sensory contribution from facial nerve as well
    • Pierce petrous bone from geniculate ganglion
    • Can extend onto TM and EAC
  • Forms a plexus on promontory
    • Sensory and vasomotor functions
    • Sensory fibres have cell bodies in glossopharyngeal ganglia and post-ganglionic symphathetic fibres come from superior cervical ganglion

Plexus gives off Lesser Petrosal Nerve

  • Contains pre-ganglionic PNS fibres
  • Derived from Inferior salivary nucleus
  • Destined for otic ganglion then supply parotid
  • Fibres enter plexus with glossopharyngeal tympanic branch
  • Leaves ME via canaliculis in anterior wall above eustacian tube
    • Runs short course in MCF
    • Emerges from a hiatus lateral to the GSPN
    • Passes thru foramen ovale to otic ganglion

Other branches of distribution of the tympanic plexus are supplied to the mucous membrane of the tympanic cavity; a branch passes to the fenestra vestibuli, another to the fenestra cochleæ, and a third to the auditory tube

108
Q

In what direction is the Modiolus of the cochlea orientated?

A
  • Base lies at the fundus of the IAM
  • Apex lies across long axis of petrous temporal bone
    • Points towards canal for tensor tympani
109
Q

What is the Pars superior?

A

Embryological division

Semicircular canals and utricle

110
Q

What is the Pars inferior?


A

Saccule and cochlea – form after pars superior

111
Q

What is the endocochlear potential?

A

Electrolyte gradients result in potential differences between the compartments and result in electrochemical potentials

Scala media is +80mV (this is the endocochlear potential)

Scala vestibule is+5mV

Scala tympani is 0mV

112
Q

How is endocochlear potential maintained?

A

Maintained by stria vascularis

113
Q

What is the chemical composition of endo + perilymph?

A

Endolymph

  • High potassium and low sodium
  • Same protein content as CSF
  • High mucopolysaccharide content
  • Produced by marginal cells of stria vascularis (Na/K ATPase)
      • Ampulla and maculae of utricle and saccule
  • Reabsorbed via radial flow at stria vascularis and longitudinal flow in the ELS
  • Low concentration of Na+ maintained by epithelial Na channel – found in stria vascularis, spiral prominence, spiral limbus, spiral ligament and spiral ganglion

Perilymph

  • High sodium and low potassium
114
Q

Draw the tonotopic arrangement of the cochlear?

A
115
Q

Where is the basilar membrane stiffest & widest?

A

Base, Apex

116
Q

Describe the embryology of the inner ear

A

3rd week

  • neuroectoderm and ectoderm lateral (dorsal) to 1st branchial groove, on the lateral aspect of the neural tube condense to form the otic placode (day 22)

4th week

  • otic placode invaginates to become the otic pit then otocyst/otic vesicle (day 30)

5th week

  • otic vesicle develops a wide dorsal (lat) utricular and slender ventral (medial) saccular parts
  • endolymphatic sac and duct develops medially (cranially) between these (first to appear and last to develop) à straight during 1st half of term àwhen fully formed (midterm) extends from junction then through vestibule posteromedial and parallel to common crus à through vestibular aqueduct à later stages curved to turn downwards at 30-60 degrees

Neurogenic foci are formed within otic epithelium and produce the statoacoustic ganglion à send axonal projections into areas of developing auditory and vestibular sensory receptors peripherally and brain nuclei of pathways centrally

6th week

  • semicircular canals appear (S > P > L)
  • Day 35 SCC develop, initially as flattened pouches then as canals at 6/40 à opposite epithelial walls meet and fuse à obliterated centrally

7th week

  • formation of basal turn of cochlear
  • A medial pouch of the saccule forms the cochlear duct, 1 coil at week 8, 2 week 10, 2 & 1/2 by 25/40. Ductus reuniens forms the connection à lengthens and narrows

8th week

  • Pars superior = semicircular canals and utricle fully formed. Followed by pars inferior = saccule and cochlear formation
  • condensation and differentiation of mesenchyme around the otic vesicle forms the cartilaginous otic capsule. Vacuoles appear to form the perilymph space. Later ossifies to become the osseous labyrinth
  • perilymph space formation starts at 8/40, completed by 16/40 à first vestibule, then cochlear duct (scala tympani >vestibule) à produced through reabsorption of cartilage that surrounds membranous duct
  • stria vascularis forms

11th week

  • vestibular end organs formed
  • Maculae develope from epithelium at areas where nerves enter the saccule and utricle; sensory cells (stereo and kinocilium) and supporting cells (produce otoconia and gelatinous layer of otoconial membrane). Otoconia are multilayered calcium carbonate. Adult form by 14-16/40.
  • Cristae form on convex side of the SCC at the ampullae as a ridge of sensory and supporting cells. Cupula present at 24/40 (reaches the walls of the ampulla).

12th week

  • cochlear (2.5) turns complete

15th week

  • membranous labyrinth minus end-organ is complete -
  • Otic capsule forms from mesenchyme (cartilage model) weeks 8-16 à which also forms the perilymph spaces around the vestibule then scala tympani, then scala vestibuli. Ossification in 14 centres begins in 15-16/40 (basal turn), last centre does so at 21/40 (i.e. full size at 5/9). Ossification centres are trilaminar without areas of epiphyseal growth. There is no remodelling. No suture lines à fusion of centres peripherally without intermediate zones of epiphyseal growth. Blood supply of otic capsule is the stylomastoid artery which forms part of the tympanic plexus. Membranous labyrinth blood from branches of the labyrinthine artery à established by 4/12 (prior to ossification)
  • Trilaminar structure = outer periosteum, inner periosteum, middle layer = combined intracondral and endochondral bone (replaces marrow) à independent timetable of growth for each layer of centre of ossification
  • Subarcuate fossa = root for erosive vascular buds that cause canalicular division of capsule to be spongy à increase in arcs of SCC after growth cease in cochlea/vestibular divisions of capsule à reduced after 5/9

20th week

  • stria vascularis (develops from ectoderm of otocyst – melanocytes from neural crest) and tectorial membrane complete

23rd week

  • ossification complete. Last area is the fistula ante fenestrum (? Site of cartilaginous rests that are involved in pathogenesis of otosclerosis – transcapsular channel)
  • membranous (minus endolymphatic sac) and bony labyrinth complete
  • * inner ear is fully developed at birth
117
Q

In what order do the SCCs develop?


A

Superior

Posterior

Lateral

118
Q

What is the Jackler classification of inner ear malformations?

A

Classification of Congenital Inner Ear Malformations

Malformations Limited to the Membranous Labyrinth

Complete membranous labyrinthine dysplasia

Limited membranous labyrinthine dysplasia

Cochleosaccular dysplasia (Scheibe)

Cochlear basal turn dysplasia

Malformations of the Osseous and Membranous Labyrinth

Complete labyrinthine aplasia (Michel)

Cochlear anomalies

Cochlear aplasia

Cochlear hypoplasia

Incomplete partition (Mondini)

Common cavity

Labyrinthine anomalies

Semicircular canal dysplasia

Semicircular canal aplasia

Aqueductal anomalies

Enlargement of the vestibular aqueduct

Enlargement of the cochlear aqueduct

Internal auditory canal anomalies

Narrow internal auditory canal

Wide internal auditory canal

Eighth nerve anomalies

Hypoplasia

Aplasia

119
Q

How else can you classify inner ear malformations?


What are the membranous deformities?

A

>90% of congenital deafness

No abnormality seen on CT (Bony labyrinth normal)

120
Q

Mondini’s malformation What is it?

A
  • Incomplete partitioning of the cochlear due to arrested development during 7th week
  • 55% of osseomembranous anomalies
  • Radiology
    • 1 ½ turns
    • Cochlear smaller than usual
    • Lacks an interscalar spetum in the upper turns
    • Vertical height of cochlea 6-8mm (Normally 8-10)
    • Apical scala communis secondary to deficiency of osseous spiral lamina
  • Organ of Corti and neural population development is variable
    • Hearing variable
  • SCC anomalies in 20%
  • Commonly associated with EVA and stapes footplate anomalies à predispose to perilymph fistula and meningitis
  • CN VII anomalies when stapes anomalies present à displacement of second genu ant and inf
  • Subtypes into 3 variants
    • Type 1 = lacks modiolus and demonstrates cystic appearance
    • Type 2 = normal base but a cystic apex
    • Type 3 = deficient modiolus and partial interscala septation
121
Q

What syndromes are associated with Mondini?

A
  • Pendred, Wardenburg’s, Treacher-Collins, congenital CMV
122
Q

Where does the vestibular aqueduct develop from?

A

Endolymphatic sac and duct develops medially (cranially) between utricle and saccule (first to appear and last to develop)

123
Q

When does the vestibular aqueduct develop?

A

Week 5

124
Q

What is EVAS?


A

Enlarged Vestibular Aqueduct Syndrome

125
Q

What is the petrosquamous sinus (of Luschka)?

A

Is a fetal vein that generally disappears by birth [1] and, when present, runs backward along the junction of the squama and petrous portion of the temporal, and opens into the transverse sinus

126
Q

Describe the auditory pathway 


A
  • Afferent neurons commence at the base of IHC’s and OHC’s
    • Bipolar in nature à short processes receive synapses from cochlear hair cells, longer proximal processes join together to form cochear nerve
    • Central projection is the auditory nerve
    • Cell bodies reside in the Spiral Ganglion – “Spiral ganglion cells”
  • Afferent auditory neurons have a Tonotopic organization
  • Carries information regarding which fibres are responding to sound, rate and timing of response
  • Nerve travels along the IAC to the IAM and terminates at the cochlear nucleus
127
Q

Brainstem and Midbrain

A

Cochlear nucleus

  • Pontomedullary junction of dorsolateral brainstem
  • Initial relay station
  • Multiple cell types within subdivisions
  • Tonotopic organization maintained
    • High frequencies dorsal
    • Low frequencies ventral
  • Projection from the cochlear nucleus is to
    • Superior Olivary complex
    • Lateral lemniscus nuclei
    • Inferior colliculus
  • Brainstem auditory processing allows sound localization via assessment of timing and intensity
  • Central synapses are vulnerable to sensory deprivation
128
Q

Superior Olivary Complex

A
  • Medial to cochlear nucleus within the Pons
  • Integrates information from both cochlear nuclei
    • Role in localization of sound
    • Role in efferent pathways
  • Fibers from both cochlear nuclei radiate to the SO nucleus via the trapezoid body (Ventral Stria)
  • First point in afferent auditory system at which same neuron receives input from both ears à binaural inputs and sound localisation
129
Q

Lateral Lemniscus

A
  • Prominent auditory tract from the cochlear nucleus to the contralateral Inferior colliculus
  • Multiple branches to the superior olivary complex and nuclei of the lateral lemniscus
130
Q

Inferior Colliculus

A
  • Midbrain
  • Processes frequency specific information
  • Receives information from the cochlear nucleus, superior olivary complex and lateral lemniscus, somatosensory system, visual and vestibular systems
  • Processes this information and projects on to the medial geniculate body of the thalamus
  • 10X the number of fibres in the auditory nerve (250K)
131
Q

Thalamus and Auditory Cortex

A

Medial geniculate body in the thalamus

  • Relay centre for auditory information from the inferior colliculus
  • No increase of freq of discharge with increasing intensity
  • Also has significant input from the auditory cortex

Auditory cortex

  • Tonotopic organization
  • Enables language comprehension
  • Receive auditory input from both ears
  • Primary auditory Cortex
    • Located in Heschl’s gyrus within the temporal lobe, close to the sylvian fissure
    • Brodman’s Area 41
    • Tonotopic with higher frequencies medially
    • Integrates and processes auditory signal (language comprehension)
  • Asociation Auditory Cortex
    • Brodman areas 22/42
    • Lateral to primary cortex
    • Part of Wernicke’s Area (Language reception)
    • Important in speech perception
132
Q

How does auditory pathway relate to the waves of ABR

A

Cummings (Moller et al)

ECOLI ?(Outdated)

Ponton et al

Wave I

CN VIII within IAM

Distal CNVIII

CN VIII within IAM

Wave II

CN VIII intracranial portion

Cochlear nuclei (C)

CN VIII intracranial portion

Wave III

Cochlear nucleus complex

Superior olivary nucleus (O)

Axons from cochlear nuclei to ventral acoustic stria

Wave IV

Superior Olivary Complex

Lateral lemniscus (L)

Ascending axons from cochlea nuclei

Wave V

Lateral Lemniscus

Contralateral inferior colliculus (I)

Ascending axons from cochlea nuclei

133
Q

What is the resonance of the Pinna? 


A
  • F at which a mass vibrates with the least amt external force
  • Determined by elasticity, mass and frictional characteristics of the medium
  • 2000-5500 Hz
134
Q

What is the resonance of the EAC?

A

3000Hz

135
Q

What is the resonance of the ME?

A

800-5000 Hz (mostly 1-2kHz)

136
Q

What is the resonance of the TM? 


A

TM = 800-1600Hz

137
Q

What are the 4 mechanisms used for sound localisation?

A

Interaural amplitude differences

  • Differences in interaural sound pressure due to baffle and (Mainly) shadow effects

Shadow effect

  • Sound from one side is attenuated by the head
  • Sounds of shorter wavelength have their pressures reduced on the other side of the head

Baffle effect

  • Sounds striking the side of the head will be reflected to some extent
  • Interaction of reflected and incoming pressure waves can increase sound pressure

Interaural time latency differences

138
Q

What is the transformer ratio theory?


A

A sound pressure wave traveling through air must be converted into a fluid pressure wave at the oval window

This air-fluid impedance mismatch results in 99.9% of the sound pressure being reflected (equivalent to a 30dB reduction in SPL).

Middle ear transformer is designed to overcome this mismatch by increasing the pressure at the oval window (at the expense of velocity of movement)

Tympanic membrane to stapes footplate surface area ratio

  • Average TM area is 69mm2 – gathers force over its entire surface
  • Average footplate area is 3.4mm2
  • Ratio is approx 20:1
  • This mechanism is theoretically responsible for 26dB SPL increase at the footplate cf at the TM (because pressure is force/area)
139
Q

What are the middle ear levers?

A

Refers to the difference in lengths of the manubrium of the malleus and the long process of the incus

  • Ratio of length of malleus handle to incus long process is 1.3:1
  • Small force on the manubrium of the malleus leads to a larger force on the long process of the incus

Malleus and incus rotate in the coronal plane around a fulcrum which passes through the anterior malleal ligament and the incudal ligament

This results in a lever action of the ossicles with decreased displacement but increased pressure

Adds approx 2.3dB to SPL at oval window cf TM

140
Q

What is carhart’s notch? 


A

Increase in bone conduction threshold at 2kHz

141
Q

What is the mechanism for carhart’s notch?


A

is due to impairment of the inertial and radiation elements of bone conduction by the stapes fixation

142
Q

Draw the pathway for the stapedial reflex

A
  • CN VIII
  • Ventral cochlear nucleus
  • Trapezoid body
  • Bilateral projection to superior olivary complex
  • Medial portion of the facial motor nucleus
  • Facial nerve
  • Nerve to stapedius
  • Stapedius muscle
143
Q

At what threshold does stapedial reflex occur? 


A

85dB

Acoustic reflex threshold à determines softedt sound which will elicit a stapedius contraction à normally 70-100dB HL

144
Q

Which hair cells does stapedial reflex test?

A

Inner

145
Q

What is the Maximal conductive loss? 


A

60dB

Acoustic coupling is 60dB less than ossicular coupling

146
Q

Maximal conductive loss due to a perforation only?

A

Normal hearing to 50dB CHL à caused by loss of sound pressure difference across TM

Reduces effective area of TM in contact with sound wave, reduces pressure differential across TM and reduces mechanical coupling

Determined by:

  • Size of perforation
    • Larger perforations produce greater CHL
    • Lose pressure differential between EAC and middle ear therefore TM doesn’t move as much and get reduced ossicular coupling
  • Volume of middle ear and mastoid
    • When combined volume is less than 0.4cm3 get increased CHL
    • Average volume is 6cm3 (normal range 2-20cm3)
    • Smaller ME spaces result in larger AB gaps
  • Frequency
    • Greater CHL at lower frequencies

Not determined by position of perforation

Acoustic coupling is increased in the presence of a perforation, therefore maximum CHL is 50dB

147
Q

What are the functions of the OHCs?

A
  • Tonotopicity
  • Increase sensitivity at particular frequency by increasing magnitude of traveling wave
    • Performed by the mechanical properties of the OHCs ie contraction or elongation of OHCs in response to depolarization or hyperpolarization
    • Actions lead to altered properties of the basilar membrane
    • Highly viscous aqueous environment that hair bundles in dampens their motion and prevents resonant behavior from arising à ohc compensates for
    • Amplification of BM movement can be 100 fold or more, and the lower the stimulus size, the greater the amplification
148
Q

What is recruitment?

A
  • ‘An abnormally steep growth in loudness with increased intensity’
  • ‘An audiologic phenomenon whereby the perceived intensity of increase in a sound is greater than the actual increase in intensity’
  • Seen in cochlear hearing loss
  • Thought to be due to a loss of outer hair cells with preservation of inner hair cells – therefore when stimulus gets above 50dB and starts to directly stimulate the inner hair cells they still have their neural connections and suddenly begin to respond
  • Practical application of this is that to amplify sound with an aid you may need significant amounts of amplification to perceive softer sounds but louder sounds are also amplified and may be too loud
149
Q

Describe the blood supply of the inner ear 


A
  • Main supplyà Internal auditory (labyrinthine) artery
    • Mostly (45%) from the ant inf cerebellar art, sup cerebellar art or the basilar artery.
    • à 2 branches shortly after entering the IE (inner ear): anterior vestibular art and the common cochlear art.
  • Ant vestibular artery à utriculus and sup and lat ampullae, and small portion to the sacculus.
  • Common cochlear artery à 2 branches
    • Proper cochlear (or spiral modiolar) artery
    • Vestibulocochlear artery
      • Cochlear branch
      • Posterior vestibular branch à major supply to the posterior ampulla, sacculus and the parts of the utriculus and horiz and sup ampullae.
150
Q

Draw a cross section through a SCC

A
151
Q

Draw a cross section through the ampulla of the SCC


A
152
Q

Draw a cross section through the macula of the utricle / saccule 


A
153
Q

Draw a cross section through otolithic membrane

A
154
Q

What is the orientation of hair cells in the saccule? 


A

Saccular kinocilia point away from the striola

Saccular maculaà oriented in the vertical plane

155
Q

What is the orientation of hair cells In the utricle?

A

Utricular kinocilia point towards the striola

Utricular maculaà oriented in the horizontal plane

156
Q

In the SCCs, in which direction is flow excitatory?

A

LSCC – amupullopetal – towards

PSCC, SSCC – ampullofungal - away


157
Q

What is the orientation of the SCCs?


A
158
Q

How much of a full circle do SCC make? 


A

Almost complete circle, >than 180

159
Q

What are the layers of the labyrinth? Bony

A
  • endosteal, enchondral, and periosteal layers
  • endosteal layer consists of bone lined with a single thin layer of cells that have numerous gaps that separate them
  • enchondral layer is unique in that it reaches adult size by 23 weeks’ gestation and undergoes minimal remodeling after age 2 years à layer for otosclerosis
  • periosteal layer consists of lamellar bone and is capable of remodeling and repair à in fracture of labyrinth only periosteal may repair à fibrous tissue
160
Q

What are the layers of the labyrinth? - Membranous?


A
  • Outer Fibrous vascular layer
    • Adherent in places to endosteum
    • Forms stria vascularis and produces endolymph
  • Intermediate layer
    • Homogenous similar to a basal lamina
  • Inner Epithelial Layer
    • Contains receptors for balance and sound
    • Mostly low epithelium in other areas
  • in maculæ of the utricle and saccule, and in the transverse septa of the ampullæ of the semicircular ducts, the middle coat is thickened and the epithelium is columnar, and consists of supporting cells and hair cells
  • supporting cells fusiform, and their deep ends are attached to the membrana propria, while their free extremities are united to form a thin cuticle
  • hair cells are flask-shaped, and their deep, rounded ends do not reach the membrana propria, but lie between the supporting cells
  • deep part of each contains a large nucleus, while its more superficial part is granular and pigmented
  • free end is surmounted by a long, tapering, hair-like filament, which projects into the cavity
  • filaments of the VIII enter these parts, and having pierced the outer and middle layers, they lose their medullary sheaths, and their axis-cylinders ramify between the hair cells
161
Q

Draw the pathway for the VOR 


LSCC

A
162
Q

Draw the pathway for the VOR 


PSCC – C (below)

Draw the pathway for the VOR 


SCCC - B (below)

A
163
Q

Draw the medial wall of the labyrinth

A
164
Q

Describe the ossification of the labyrinth

A
  • Otic capsule forms from mesenchyme (cartilage model) weeks 8-16 à which also forms the perilymph spaces around the vestibule then scala tympani, then scala vestibule
  • ossification in 14 centres begins in 15-16/40 (basal turn), last centre does so at 21/40 (i.e. full size at 5/9)
  • ossification centres are trilaminar without areas of epiphyseal growth. There is no remodelling. No suture lines à fusion of centres peripherally without intermediate zones of epiphyseal growth.
  • Blood supply of otic capsule is the stylomastoid artery which forms part of the tympanic plexus.
  • Membranous labyrinth blood from branches of the labyrinthine artery à established by 4/12 (prior to ossification)
  • Trilaminar structure = outer periosteum, inner periosteum, middle layer = combined intracondral and endochondral bone (replaces marrow) à independent timetable of growth for each layer of centre of ossification
165
Q

What are the segments of the facial nerve? Lengths?

A
  • Intracranial: 20mm
  • IAC: 8mm
  • Labyrinthine: 4mm
  • Tympanic: 12mm
  • Mastoid:16mm
166
Q

Branches VII ?

A

Greater superficial petrosal nerve

  • Runs anteriorly from the geniculate ganglion, initially in the canalis hiatus facialis, then along floor of MCF outside the dura

Nerve to stapedius

  • From the mastoid portion of the nerve as it begins it’s descent
  • Reaches muscle via a canal in the pyramid

Chorda tympani

  • Contains taste fibers from the anterior 2/3 of the tongue and pre-ganglionic parasympathetic fibers for the submandibular and sublingual glands
  • Runs anteriorly and superiorly from mastoid portion of nerve, medial to annulus and passes lateral to long process of incus and medial to handle of malleus à canal of Huguier

Sensory auricular branch – supplies sensation to external ear

Post-auricular branch

  • Runs from region of stylomastoid foramen to supply auricularis posterior and the occipital belly of occipitofrontalis
  • Has communications with CN IX and X

Muscular branch

  • Supplies posterior belly of digastric and stylohyoid

Temporal branch

  • Emerges from upper border parotid
  • Runs across zygomatic arch
  • Supplies anterior and superior auricular mm, frontalis, orbicularis oculi, corrugator

Zygomatic branch

  • Upper and lower parts which pass above and below the eye
    • Upper to frontalis and upper orbicularis oculi
    • Lower to Lower half orbiculari oculi and muscles below orbit (Buccinator)
    • Some branches pass to both upper and lower lids
  • Paralysis prevents blinking, tear spread and increases risk of corneal ulceration

Buccal branch

  • Supplies orbicularis oculi, buccinator, orbicularis oris, zygomaticus, levator anguli oris

Marginal mandibular branch

  • Runs anteroinferiorly, below angle of mandible, under platysma
    • Passes below mandible angle in 20%
  • Turns upwards and crosses mandible
    • Typically crosses facial artery and vein
  • Supplies orbicularis oris and other mm of lips and chin

Cervical branch

  • Supplies platysma
  • Marginal branch can arise from this branch within the neck
167
Q

Blood supply VII?


A
  • Posterior fossa – twigs from AICA
  • In IAC: Labyrinthine artery from AIC artery
  • Facial canal – stylomastoid and petrosal arteries which anastamose at 2nd genu
  • Parotid gland – stylomastoid, post auricular or occipital, superficial temporal, transverse facial
  • Superficial petrosal artery from middle meningeal artery
  • Stylomastoid artery from posterior auricular artery
  • Transverse facial, superficial temporal, facial a
  • ?Anastamosis of vessels is in region of geniculate ganglion which may make the geniculate ganglion more vulnerable – watershed area
  • No anastomoses with labyrinth segment, others anastamose freely
168
Q

Draw the intratemporal course of the facial nerve (label the lengths and angles)

A
169
Q

What angles does VII make at the Meatal foramen

A

132

170
Q

What angles does VII make at the Geniculate ganglion?

A

75

171
Q

What angles does VII make at the 2nd genu?


A

124

172
Q

What angles does VII make at the Mastoid segment?

A

Runs vertically down, slightly posteriorly and laterally (5-35 degrees from vertical plane)

173
Q

What is the diameter of the VII meatal foramen?


A

0.68mm

174
Q

Between what structures does the labyrinthine segment VII run?

A
  • Cochlea anteriorly, superior SCC posteriorly and vestibule beneath
175
Q

What are the variations of the facial nerve?


A
  • Tympanic segment
    • Superior to SCC
    • Bifurcation near OW
    • Nerve overlies OW
    • Thru stapedial artery
    • Runs posterior between OW and RW
    • Inferior to RW
    • Mastoid Segment
      • Abnormal course of a normal nerve
      • Bifurcation and trifurcation distal to OW
      • Hypoplasia
176
Q

What is the definition of a dehiscent nerve?


A

Any discontinuity in the bony structure of the fallopian canal producing abnormal communication between the middle ear space or mastoid air cell and facial nerve

177
Q

What is the incidence of dehiscence of VII? Where do they occur?

A
  • May be dehiscent in 30-50% temporal bones
    • 90% in tympanic segment, 9% in mastoid segment
    • 80% over oval window - ?most frequent site
    • 22% multiple dehiscences
178
Q

Describe the path of the chorda tympani nerve

A
  • Arises ~6mm above stylomastoid foramen
  • Leaves facial trunk and takes recurrent course upward and forward in canaliculus
    • Average 5.3mm above stylomastoid foramen (1.5 – 10.9mm)
    • 2% Extratemporal origin
  • Enters tympanic cavity through posterior wall (post tympanic canaliculus), lateral to pyramid
  • Runs forward over pars flaccida, behind the neck of the malleus
  • Leaves ME at anterior margin of tympanic notch – lying between tympanic part and that part of tegmen tympani which walls in canal for tensor tympani – canal of Huigier
  • Emerges from petrotympanic fissure
  • Grooves medial side of spine of sphenoid
  • Joins lingual nerve ~2cm below BOS
  • Tiny rami communicans with otic ganglion - ? secretomotor supply to parotid
  • Parasympathetic secretomotor fibres relay in SM ganglion è SMG + SLG
179
Q

Variations of Chorda tympani’s course?


A

2% extratemporal origin – can arise as high as LSCC

The chorda tympani may run independently of the lingual nerve after its exit from the petrotympanic fissure.

Can run lateral to malleus/TM

It has been observed attached to the inferior alveolar nerve until the latter entered the alveolar canal; the chorda tympani then supplied the salivary glands and joined the lingual to supply the tongue.

180
Q

What are the surgical landmarks in the mid fossa approach?

A
181
Q

What are 3 ways for finding the IAC in the mid fossa approach?

A
  1. External auditory canal
    • EAC is parallel to IAC and the 2 canals coincide
    • Drilling is commenced in the most medial part of straight line ∥ to EAC and ⊥ to the inner table (median petrous apex ridge)
    • Safe distance @ fundus is 2.4 mm & at porus/medial IAC is 25 mm
  2. Drilling tegmen to identify malleus head (Catalano)
  • It has been shown to be consistent measurement, although it is undesirable to create an additional communication b/w MCF & middle ear with potential for CSF leak/infection.
    1. Relationship between GSPN & superior semicircular canal
  • Angle b/w superior semicircular canal and GSPN is 1000 with little variability
  • IAC bisects this angle
  • Apex of this angle overlies vestibular area
  • GSPN leads to geniculate ganglion and labyrinthine facial canal. Exposure of latter puts cochlea at risk as it is ≤ 1mm from labyrinthine facial n.
182
Q

What is the course of a persistent stapedial artery?


A

Arises from ICA

Passes through obturator foramen of stapes

Turns anteriorly à ends by replacing middle meningeal artery or branching into supraorbital, infarorbital and mandibular arteries to accompany V3

183
Q

What are the vestibulofacial communications?

A

Some of the superior and inferior vestibular nerve bundles may receive fibres from the facial in IAC

Facial vestibular anastomoses of Rasmussen between the intermediate and vestibular nerves

  • Represents fibres of nervus intermedius that run in superior vestibular nerve and join nervus intermedius via vestibulofacial anastomosis
  • ? PNS supply to labyrinth

*RACS ENT Fellowship (19 decks)

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